1. Field of the Invention
The present invention relates to a spindle motor for use in a disk drive apparatus.
2. Description of the Related Art
In recent years, in accordance with increased storage density of disks, there has been a demand for disk drive apparatuses, such as, for example, hard disk drives, to control rotation of the disks, movement of heads, and so on with high precision. In a known hard disk drive (HDD) disclosed in JP-A 2006-40423, a gas arranged in an interior of the HDD is a low-density gas, such as, for example, a helium gas or a hydrogen gas, and the HDD is thus arranged to achieve a reduction in resistance of the gas against a disk, a head, and so on during rotation of a spindle motor. The reduction in the resistance of the gas against the disk, the head, and so on contributes to reducing vibration of the disk, the head, and so on, enabling highly precise data recording.
In the case where the interior of the HDD is filled with a gas such as a helium gas or the like, the helium gas, for example, which has extremely small molecules, tends to easily leak out of the interior of the HDD to an outside of the HDD through a slight gap. Here, a fluid bearing mechanism having a so-called partially-filled structure is sometimes employed in a spindle motor (hereinafter referred to simply as a “motor”) installed in the HDD. A motor including a fluid bearing mechanism having the partially-filled structure is described in, for example, JP-A 2006-40423. In a motor having such a fluid bearing mechanism, it is desirable to make air pressure substantially uniform in a space in which fluid surfaces are defined. Accordingly, a shaft of such a motor sometimes includes an airway arranged to join an extra-bearing space to an intra-bearing space in a housing of the motor.
As disclosed in JP-A 2012-152098, for example, a middle gap 63 is arranged to be in communication with a space below a bearing mechanism 4 through a first communicating portion 411a, a hole portion 411, and a second communicating portion 411b. Air pressure in the middle gap 63 is thus arranged to be substantially equal to air pressure in an interior space 143 of a disk drive apparatus 1. As a result, a balance between upper and lower surfaces of a lubricating oil 49 held in a first inclined gap 64 is maintained in a substantially constant state.
The airway is defined by, for example, drilling into an end surface of the shaft using a drill or the like. If the airway is brought into communication with a space other than destination spaces of the airway, such as, for example, a screw hole defined in the shaft, the gas inside the HDD may leak out through the airway.
The present invention has been conceived in view of the above problem to prevent a gas inside of a housing from leaking out of the housing through an airway.